1. Field of the Invention
The present invention relates to the use of gas within land-fill sites, the recycling of materials from recycling collection and separation, and the recycling or commercial use of waste effluents materials from land-fills.
2. Background of the Art
A significant societal effect caused by the unceasing growth in world human population is the increased use of a limited supply of raw materials. Both in the field of agricultural and the field of commercial products, an increasing population requires an increasing expenditure of energy and use of material to sustain even the existing average life style. As desires and expectations are growing around the world within every population center for higher standards of living, there is a multi-faceted draining effect on resources. Increased production capacity has been able to sustain this growth for centuries, but even the most optimistic technologist must appreciate that there is a finite limit to growth and production given the closed system of the Earth.
Recycling has been one direction of increased effort in reutilization of materials to conserve dwindling original supplies. Initially, recycling involved the wholesale reuse of objects, such as beverage containers where return fees or deposits were placed on the containers, the fees were returned to the purchaser with return of the containers, and the containers were cleaned and returned into the production line to be refilled. The limitations on this system included at least the facts that the containers would show unacceptable levels of wear fairly early during repeated reuse (especially with bottles that could be easily scratched or chipped), containers had to be returned to individual original suppliers according to brand names (which dictated against any centralized system), and cleaning was difficult as different co-wastes were added to the containers (e.g., cigarette stubs and filters) and few viable cleaning processes could remove some of the associated wastes without extensive manual labor.
One of the more successful recycling programs has involved the recycling of aluminum beverage containers. The success has been accomplished because of some unique attributes in the specific product. The material itself (the aluminum) is easily melted and placed back into the natural manufacturing stream. Associated materials in the product (e.g., inks, coating materials, lid adhesives, and the like) are easily removed from the aluminum by the heating needed to melt the aluminum (and with possible solvent treatment), and solid wastes added to the aluminum containers can be removed by physical processes (e.g., shredding of cans and washing/flotation) alone or in combination with the melting steps needed for recycling. This model, however, does not translate well to other materials, as the properties, economics, technology and market for aluminum are unique, and it is this uniqueness that enables success of the system.
Certain classes of polymeric materials are presently recycled in commercial systems relying in great part on collection of polymeric containers from residential and commercial sites. This system is complicated in that associated wastes with differing sources of polymeric materials may not be amenable to a single format of treatment. Although local jurisdictions may require some level of cleaning of the polymeric containers, the original liquids or powders may be insufficiently removed from the polymer. These materials may vary from water, beverages, detergents, oils, alkaline cleaners, and highly toxic materials, including pesticides. In addition, the containers may contain labels that are applied by adhesives of different strengths, and the label stock itself may need to be treated by distinct processes. A single cleaning process has been unlikely to act on all polymeric containers, at least in part because of the deficiencies in the cleaning steps that fail to provide a sufficiently pure supply of polymer that would enable direct recycling.
Recycling of motor oil containers is illustrative of the problem. Motor oil containers typically are high-density polyethylene (HDPE) which lends itself well to recycling if it is sufficiently clean. However, residual oil coating the interior surface of the “empty” motor oil containers constitutes a contaminant that prevents use of the containers as high grade plastics. Based upon measurement of samples of used motor oil containers, this residual oil coating appears to average 4.6 percent of the weight of the used plastic container and can represent as much as 20 percent of the container weight. Estimates are that over one billion one-quart plastic containers were filled with motor oils in the United States in 1993. If 4.6 percent by weight of those containers is motor oil, the one billion empty plastic containers represent approximately 160 million pounds of plastic and over 7 million pounds of motor oil that could be recovered for reuse if an appropriate separation method were available. However, because the motor oils have not been easily separated from the plastic containers, the vast majority of these containers are currently disposed of in landfills, leaking oils into the soil and groundwater, and occupying significant landfill volume.
Current available options to landfilling the waste plastics include (a) grinding the containers and using them in other plastic recycling processes on a very limited (dilute) basis; (b) using an aqueous process to displace the oil from the plastic; (c) using a halogenated solvent to dissolve/dilute the oil; or (d) using a combustible or flammable solvent to dissolve/dilute the oil from the plastic.
The problems with these options are as follows:
a. Existing recyclers in the United States can blend limited quantities of oil contaminated plastics in recycled plastic products. Large quantities cannot be blended because of the undesirable effects of the residual oil on the recycled plastic properties. Examples include “plastic lumber” and lower grade plastic products.
b. Aqueous processes can be used to displace the oil from the plastic. However, detergents and/or surfactants are required to assist displacement of the oils. A stream of usable oil-free plastic will be generated by this method; however, the displaced oil will be contaminated or changed chemically and additional processing will be needed to separate it from the aqueous solutions. The aqueous solutions themselves will be a secondary waste stream that will require treatment before being recycled or discharged as waste water.
c. Halogenated solvents can be used to dissolve/dilute the oils from the plastic. Again, usable plastic will be obtained by this process if the solvents do not extract essential components from the plastic. The halogenated solvent solutions will require distillation to recover the oils and recycle the solvents. In general, it is difficult to fully reclaim usable oil from the distillate. Furthermore, many halogenated solvents are ozone depleting compounds and potential health hazards to humans, and therefore their use and release into the environment are under regulation and close scrutiny by federal and state governments.
d. Combustible or flammable solvents may be used to dissolve and/or displace the oil from the plastic. Usable plastic can be generated by this method if the solvents do not extract essential components from the plastic. The combustible or flammable solvent solutions will require distillation to recover the oils and recycle the solvents. Only distillation equipment suitable for combustible or flammable solvents may be used and even then fire safety concerns will be significant. As in the case of the use of halogenated solvents, the oil may not be fully recoverable from the distillation.
The methods described above can provide some usable plastic from oil-contaminated plastics. However, they will provide usable oil only at the expense of a secondary waste stream that itself will require treatment and additional expense. The recycling of plastic and oil from “empty” plastic oil containers presents serious environmental and waste stream disposal problems if conventional organic or aqueous solvents are used for the separation of the plastic and oil. Discarding of the containers as landfill waste also presents environmental problems in that the residual oil may eventually leach into soil and groundwater.
Landfills provide the most complex issue to be faced in the entire realm of waste disposal, with the possible exception of long-term storage of nuclear wastes. Landfills are little more than holes in the ground into which massive volumes of wastes are dumped, compacted and covered, with an unsupported expectation that the material will eventually decompose and be absorbed into the normal ecology. This expectation is unsupported because excavations of earlier (19th and early 20th century) landfills have found that even paper products, including newspapers, are substantially intact (if not structurally pristine) over a time period where decomposition had been expected. Present attempts to moderate the impact of landfills have met limited environmental and limited economic success.
The typical landfill reclamation attempts have included providing gas vents into the covered masses of landfilled materials, separating out three streams of gas, the streams usually distinguished along the lines of highly volatile organic streams including methane, carbon dioxide, and commercially unsuitable mixtures of gases. The separations can be performed by various techniques selected from amongst semi permeable membranes, filtering membranes, differential condensation, differential absorption, differential solvency absorption, molecular sieves and combinations of these technologies. The non-commercial gases are often vented and flared directly in the atmosphere. The volatile hydrocarbon gas can be liquefied and used for fuels, usually with onsite condensation of the hydrocarbon gas. (The stream usually comprises at least or only methane. In some uses, other low carbon hydrocarbons such as ethane and some propane may be included in the hydrocarbon gas stream, in a separate stream, or in the waste stream, but these other hydrocarbons are usually removed as part of the residue gas stream. The hydrocarbon gas has been used for pipeline natural gas or compressed natural gas for vehicles. The carbon dioxide has also been liquefied, but has found few commercial outlets of sufficient volume as to make that product stream economically supportive of the recycling process. Part of the reason is the hesitancy of the largest volume of commercial use of carbon dioxide (carbonated beverages) to use carbon dioxide sourced from landfill waste streams in their products. The first manufacturer to use this source of carbon dioxide would be quickly attacked in the market by its competitors, even though the carbon dioxide greatly exceeds the purity required by the industry.
U.S. Pat. No. 5,279,615 discloses a process for cleaning textiles using densified carbon dioxide in combination with a non-polar cleaning adjunct. The preferred adjuncts are paraffin oils such as mineral oil or petrolatum. These substances are a mixture of alkanes including a portion of which are C16 or higher hydrocarbons. The process uses a heterogeneous cleaning system formed by the combination of the adjunct which is applied to the textile prior to or substantially at the same time as the application of the densified fluid. According to the data disclosed in U.S. Pat. No. 5,279,615, the cleaning adjunct is not as effective at removing soil from fabric as conventional cleaning solvents or as the solvents described for use in the present invention as disclosed below.
U.S. Pat. No. 5,316,591 discloses a process for cleaning substrates using liquid carbon dioxide or other liquefied gases below their critical temperature. The focus of this patent is on the use of any one of a number of means to effect cavitation to enhance the cleaning performance of the liquid carbon dioxide. In all of the disclosed embodiments, densified carbon dioxide is the cleaning medium. This patent does not describe the use of a solvent other than the liquefied gas for cleaning substrates. The combination of ultrasonic cavitation and liquid carbon dioxide may be well suited to processing complex hardware and substrates containing extremely hazardous contaminants.
U.S. Pat. No. 5,377,705, issued to Smith et al., discloses a system designed to clean parts utilizing supercritical carbon dioxide and an environmentally friendly co-solvent. Parts to be cleaned are placed in a cleaning vessel along with the co-solvent. After adding super critical carbon dioxide, mechanical agitation is applied via sonication or brushing. Loosened contaminants are then flushed from the cleaning vessel using additional carbon dioxide.
U.S. Pat. No. 5,417,768, issued to Smith et al., discloses a process for precision cleaning of a work piece using a multi-solvent system in which one of the solvents is liquid or supercritical carbon dioxide. The process results in minimal mixing of the solvents and incorporates ultrasonic cavitation in such a way as to prevent the ultrasonic transducers from coming in contact with cleaning solvents that could degrade the piezoelectric transducers.
U.S. Pat. No. 5,888,250 discloses the use of a binary azeotrope comprised of propylene glycol tertiary butyl ether and water as an environmentally attractive replacement for perchlorethylene in dry cleaning and degreasing processes. While the use of propylene glycol tertiary butyl ether is attractive from an environmental regulatory point of view, its use as disclosed in this invention is in a conventional dry cleaning process using conventional dry cleaning equipment and a conventional evaporative hot air drying cycle.
U.S. Pat. No. 6,200,352 discloses a process for cleaning substrates in a cleaning mixture comprising carbon dioxide, water, surfactant, and organic co-solvent. This process uses carbon dioxide as the primary cleaning media with the other components included to enhance the overall cleaning effectiveness of the process. There is no suggestion of a separate, low pressure cleaning step followed by the use of densified fluid to remove the cleaning solvent. As a result, this process has many of the same cost and cleaning performance disadvantages of other liquid carbon dioxide cleaning processes. Additional patents have been issued to the assignee of U.S. Pat. No. 6,200,352 covering related subject matter. Liquid carbon dioxide is usually the cleaning solvent.
U.S. Pat. No. 6,558,432 describes a textile cleaning system that utilizes an organic cleaning solvent and pressurized fluid solvent is disclosed. The system has no conventional evaporative hot air drying cycle. Instead, the system utilizes the solubility of the organic solvent in pressurized fluid solvent as well as the physical properties of pressurized fluid solvent. After an organic solvent cleaning cycle, the solvent is extracted from the textiles at high speed in a rotating drum in the same way conventional solvents are extracted from textiles in conventional evaporative hot air dry cleaning machines. Instead of proceeding to a conventional drying cycle, the extracted textiles are then immersed in pressurized fluid solvent to extract the residual organic solvent from the textiles. This is possible because the organic solvent is soluble in pressurized fluid solvent. After the textiles are immersed in pressurized fluid solvent, pressurized fluid solvent is pumped from the drum. Finally, the drum is de-pressurized to atmospheric pressure to evaporate any remaining pressurized fluid solvent, yielding clean, solvent free textiles. The organic solvent is preferably selected from terpenes, halohydrocarbons, certain glycol ethers, polyols, ethers, esters of glycol ethers, esters of fatty acids and other long chain carboxylic acids, fatty alcohols and other long-chain alcohols, short-chain alcohols, polar aprotic solvents, siloxanes, hydrofluoroethers, dibasic esters, and aliphatic hydrocarbons solvents or similar solvents or mixtures of such solvents and the pressurized fluid solvent is preferably densified carbon dioxide.
To make landfills better able to service the environment and to assist in the recycling of materials not added to the landfill mass, different technologies, processes and business models are needed.